Purple tint?

Hey!

I've been playing around with my graphics programm lately and noticed something I've not figured out yet. I created a dark gray tile, but as soon as I add it to my map in the editor, the dark grey suddenly turns a little purple. o_ô

Has anyone an idea why this is happening and how I can get rid of it?

Edit: Looking at the screenshot, I just noticed that the same effect turns my skin's hat purple-ish. How can this be? I even desaturated both tileset and skin in order to check if thats the problem, but it didn't help.